Stability and electronic structure in hexagonal beta-Al9Mn3Si and phi-Al10Mn3 crystals

The electronic structures of hexagonal beta-Al9Mn3Si and phi-Al10Mn3 are investigated through self-consistent calculations carried out using the LMTO method. This ab-initio approach is combined with an analysis of a simplified hamiltonian model for Al based alloys containing transition metal atoms. Results show a strong effect on an atomic structure stabilisation by an indirect Mn-Mn interaction mediated by conduction electrons over medium range distances (5 Angstrom and more). Both the role and position of Si atoms are explained as well as the origin of large vacancies which characterises these atomic structures. As beta and phi phases are related to Al based quasicrystals and related approximant structures, it yields arguments on the stabilisation of such complex phases.